Section 4-406 of the Uniform Commercial Code requires banks to return or make available to customers the items paid through their accounts. This is to give customers sufficient information to identify the items paid through their accounts. If items such as checks are not returned to the customer or if the items are destroyed (which banks are allowed to do), banks are required to "maintain the capacity to furnish legible copies of the items until the expiration of seven years after receipt of the items."
Many states have adopted similar laws. To keep things uniform, most national banks have adopted the seven-year rule as their policy.
Request a copy
A customer may request a copy of a check paid from the bank, i.e. you can get a copy of a processed check from your own bank, and the bank is required by law to provide in a reasonable time either the actual item or a legible copy.
Many banks are making images of checks available through their online banking service for a period of time. For example, Bank of America lets its online banking customers view copies of checks up to 180 days online.
Most banks charge a steep fee for this service (as of January 2010, Citibank mails you a copy of your check for $5 or $40.30 overnight on Saturday), which is why some personal finance writers still suggest keeping your own copies of checks if you get them back with your bank statements.